My nissan frontier of 2005 a Crew cab 6 cyl, dont go, it go but it go too slowly then i have too shut down the car and then start it again, then it start to go well for a while but when i stop again and go it happen the same thing so i have to shut down again and start it again but it happen the same thing. I want to know what is the problem

Is the check engine light on? If it is, take it to an autoparts store (Autozone, Advance Auto, etc) and get the code read. That could be almost anything.....

Just to let you know, The State of CA came down hard on autoparts store's doing doing diagnostic work on cars (e.g.. reading OBD codes) They're only licenesed to sell and test parts - not repair vehicles. Thus, starting July 2008, you have to buy an OBD code reader from an autoparts store in CA.